Method of preparing aldehydes

ABSTRACT

1. A METHOD OF PREPARING AN ALDEHYDE OF THE FORMULA   1-R1,2-R2,5-(H-CO-CH2-)-BENZENE   WHEREIN R1 IS A MEMBER SELECTED FROM THE GROUP CONSISTING OFF HYDROGEN AND ALKOXY HAVING 1 TO 4 CARBONS, R2 IS A MEMBER SELECTED ROM THE GROUP CONSISTING OF HYDROGEN, HALOGEN AND ALKOXY HAVING 1 TO 4 CARBONS, AND R1 AND R2 TOGETHER REPRESENT ALKYIDENEDIOXY HAVING 1 TO 4 CARBONS, WHICH COMPRISES THE STEPS OF SUBJECTING TO AN ACIDIC HYDROLYSIS A SULFOXIDE OF THE FORMULA   1-R1,2-R2,5-(R3-S(=O)-CH(-S-R3)-CH-CH2-)-BENZENE   WHREIN R1 AND R2 HAVE THE ABOVE MEANINGS, AND THE TWO R3 GROUPS ARE THE SAME AND EACH SELECTED FROM THE GROUP CONSISTING OF ALKYL HAVING 1 TO 4 CARBONS AND PHENYL SAID ACIDIC HYDROLYSIS BEING CARRIED OUT IN THE PRESENCE OF MINERAL OR ORGANIC PROTIC ACID HAVING A PK SMALLER THAN ABOUT 1 OR LEWIS AICDS.

United States Patent 1971, 46/27,998; June 2, 1971, 46/37,852, 46/37,853

Int. Cl. C07d 13/10 Us. or. 260-3405 2 Claims ABSTRACT OF THE DISCLOSURE A novel method for preparing substituted actaldehydes comprising subjecting a specific sulfoxide derivative to an acidic hydrolysis.

This invention relates to a novel process for producing a substituted acetaldehyde expressed by the general formula wherein R is a hydrogen atom or a lower alkoxy group, R is a hydrogen atom, a halogen atom or a lower alkoxy group, and R and R together may represent a lower alkylidenedioxy group.

Aldehydes of formula (I) are important as intermediates for the synthesis of various organic compounds. For example, p-methoxyphenylacetaldehyde is an important intermediate of Pentazocine, i.e., 2'-hydroxy-5,9-dimethyl-3-(3-methyl-2-butenyl-6,7-benzomorphan, known as a non-narcotic sedative, and other morphine type sedatives. Phenylacetaldehyde has a perfume like lilac or hyacinth, and can be used as perfume. (3,4-isopropylidenedioxyphenyl) acetaldehyde is novel substance, can, for example, be used advantageously as a starting material for the production of medicine Dopa, i.e., 3-(3',4-dihydroxyphenyl)-L-alanine and other morphine-type alkaloids.

,The method of this invention is based on a novel reaction difI'erent from the known methods of producing aldehydes, and can give aldehydes of formula (I) in high purities and yields.

The process for producing aldehydes in accordance with the present invention comprises subjecting to an acidic hydrolysis a sulfoxide having the general formula 0 R II SR (II) wherein R and R have the above meanings, and two R s are the same and represent a lower al-kyl group or a phenyl group to form an aldehyde of formula (I). 1

In the present specification, the lower alkyl, lower alkoxy and lower alkylidene groups mean groups having 1 to 4 carbon atoms.

The aldehydes of formula (I) produced by the method of this invention include, for example, i

p-methoxyphenylacetaldehyde, p-ethoxyphenylacetaldehyde, p-bromophenylacetaldehyde, phenylacetaldehyde,

(3 ,4-iso pro p ylidenedioxyphenyl) acetaldehyde, 3 ,4-methylenedioxyphenyl acetaldehyde,

( 3 ,4-ethylidenedioxyphenyl acetaldehyde,

(3 ,4-dimethoxyphenyl) acetaldehyde,

Patented Oct. 29, 1974 3,4-diethoxyphenyl) acetaldehyde, p-chlorophenylacetaldehyde, and p-iodophenylacetaldehyde.

[Especially preferred examples of the starting sulfoxide of formula (II) above include:

methyl 1-methylthio-2-phenylethyl sulfoxide,

methyl 2- (p-halophenyl)-l-methylthioethyl sulfoxide,

methyl 2- (p-methoxyphenyl)-l-methylthioethyl sulfoxide,

methyl 2-(3,4-isopropylidenedioxyphenyl)-1-methylthioethyl sulfoxide,

methyl 2-(3,4-methylenedioxyphenyl)-1-methylthioethyl sulfoxide,

phenyl 2- 3 ,4-isopropylidenedioxyphenyl)-1-phenylthioethyl sulfoxide, t

and

isopropyl 2-(3,4-dimethoxypheny1)-1-isopropylthioethyl sulfoxide. I

When the sulfoxide of formula (II) is subjected to an acidic hydrolysis, an aldehyde of formula (I) results. This reaction can be expressed by the following equation RLQCIECHO res-s12:

In other words, this reaction is a decomposition catalyzed by an acid, and the presence of water is not altogether necessary. Examples of the preferred acid are mineral acids such as sulfuric acid or hydrochloric acid, and or ganic acids such as trifluoroacetic acid or paratoluenesulfonic acid. The only requirement here is that the acid should be a protic acid having a pK smaller than about 1, and Lewis acids such as cupric chloride can also be used conveniently. From the economical point of view, hydrochloric acid, sulfuric acid or cupric chloride is preferred. Since the acid acts as a catalyst, its amount may be a catalytic amount. For example, the amount may be as small as about 0.05 equivalent based on the starting sulfoxides. Of course, larger amounts can also be used.

In order to render the operation easy, the above reaction is preferably carried out in a suitable solvent. The suitable solvent is an organic solvent which is chemically inert to the starting materials and reaction products. Examples of such solvent are tetrahydrofuran, alcohols, acetonitrile, ether, dioxane, or 1,2-dimeth0xyethane. The reaction temperature is not critical, and usually, temperatures of 0 to 70 0., preferably up to 60 C. are employed. At too low temperatures, the progress of the reaction is slow, and excessively high temperatures only result in an increase in the amounts of by-products. The reaction can proceed smoothly at room temperature, and the aldehyde can be produced within a short period of time. In order to carry out the reaction sufficiently, the reaction time should preferably be from a few hours to 50 hours, although varying depending upon the type of the starting material and the reaction temperature employed.

Isolation of the aldehyde from the resulting reaction mixture can be etfected by a conventional recovering means such as the neutralization of the acid catalyst, the removal of the solvent by distillation, the extraction with a suitable extracting solvent, or fractional distillation. One specific embodiment of recovery comprises neutralizing the reaction mixture with a weakly basic substance such as sodium bicarbonate, extracting it with an extracting solvent such as ether or methylene chloride, drying the extracted layer with anhydrous sodium sulfate, evaporating the extracting solvent, and distilling the residue. When a pure substance is required for analytical purposes for example, the resulting product is subjected to column chromatography to give pure aldehyde easily.

The above acid decomposition reaction can be carried out also in the copresence of an acetalization agent, and in this case, the aldehyde of formula (I) can be obtained in the form of the corresponding acetal. For example, when the aldehyde to be obtained is relatively unstable to the acid used as the catalyst, it is preferred that the reaction be performed in the copresence of an acetalization agent such as methyl orthoformate or ethyl orthoformate, and the resulting aldehyde is converted in situ to the corresponding acetal. After completion of the reaction, this acetal derivative, if desired, is treated with a weak acid, and can be converted again to the aldehyde.

The sulfoxide of formula (II) used as the starting material in the process of the present invention can be readily produced by reacting an alpha-halosulfoxide of the formula i R -cm-( JH-s-R wherein R R and 3 have the same meanings as described above, and X is a halogen atom, preferably chlorine or bromine; with a thiol or its alkali metal salt of the formula wherein R has the same meaning as described above, and Y is hydrogen or an alkali metal; under the alkaline conditions [see K. Ogura and G. Tsuchihashi, Chem. Commun. 1689 (1970)].

It has now been found that the sulfoxide of formula (II) can also be prepared by the following reaction. This method is novel, and is advantageous in that the material is readily available and the reaction operation is simple as compared with the above-mentioned method. This method comprises reacting a halocompound of the formula l N-Q-OHzX (III) with a compound of the formula 1? R3SCH2S R3 (IV Of the halocompounds of formula (III) used as the starting material in the above reaction, those in which R is hydrogen or a lower alkoxy group and R is hydrogen, halogen or a lower alkoxy group include, for example, benzyl halide, p-bromobenzyl halide and p-methoxybenzyl halide. These compounds are commonly used in the chemical industry as reaction agents, and are readily available. On the other hand, those compounds in which R and R together form a lower alkylidenedioxy group, for example 3,4-methylenedioxybenzyl halide or 3,4-isopropylidenedioxybenzyl halide can be readily synthesized. The 3,4-isopropylidenedioxybenzyl halide is a compound which was synthesized for the first time by the inventors of the present invention. This compound can be prepared by treating 4-methylcatechol with phosphorus pentoxide in acetone, and reacting the resulting 3,4-isoprpylidene dioxytoluene with N-bromosuccinimide or t-butyl hypochloride [K. Ogura and G. Tsuchihashi, Tetrahedron Letters, 3151 (1971)].

The compounds of formula (IV), the other material, were also synthesized for the firs time y h i e t rs of the present application. These compounds can be prepared by (a) reacting the compounds of formula wherein R and X have the meanings mentioned above with the compounds of formula R SY, wherein R and Y have the meanings mentioned above, under the alkaline conditions, or (b) oxidizing the mercaptol of formula R SCH SR The compounds of formula (IV) and the above-described methods (a) and (b) of producing them are described in detail in the copending US. Patent Application Ser. No. 211,100 filed Dec. 22, 1971, now US. Pat. No. 3,742,066.

Typical examples of the compounds of formula (V) include methyl methylthiomethyl sulfoxide, ethyl ethylthiomethyl sulfoxide, isopropyl isopropylthiomethyl sulfoxide and phenyl phenylthiomethyl sulfoxide.

The reaction of forming the sulfoxide of formula (II) from the compounds of formulae (III) and (IV) is carried out in the presence of a metalating agent.

Metalation has been known as the process of attaching a metal atom to a carbon atom of an organic molecule, and the metalating agent is a reagent used in the metalation. The use of a metalating agent in the present invention induces the replacement of one hydrogen atom on the methylene group interposed between the sulfoxide group and the sulfide group in the compound of formula (IV) by an alkali metal. Suitable metalating agents include, for example, alkali metal hydrides such as sodium hydride and alkylor aryl-alkali metals such as methyl lithium, butyl lithium and phenyl lithium.

The amount of the metalating agent to be used is about an equivalent to the starting sulfoxide.

The above reaction is preferably carried out in the presence of a solvent. Suitable solvents are aprotic solvents which are chemically inert to the metalating agent, and include, for example, tetrahydrofuran, dimethoxyethane, ethyl ether, dioxane, dimethyl formamide, or benzene. Since the compound of formula (IV) itself has a dissolving action, the reaction can be performed without using a solvent but using an excess of the compound of formula (IV). The reaction temperature that can be employed is from C. to +70 C. However, temperatures in the range of 0 to 30 C. are especially preferred because no heating or cooling means is necessary, and usually the reaction is carried out at room temperature. The reaction time, although varying according to the reaction conditions, is from about one hour to about 30 hours.

Isolation of the compound of formula (II) from the resulting reaction mixture can be performed by a customary method. For ease of the isolation operation, it is convenient to add methylene chloride, chloroform, or carbon tetrachloride, for example, to the reaction mixture to precipitate by-products such as alkali halides, remove the precipitate by filtration, and remove the solvent from the filtrate by evaporation at reduced pressure.

Where the aldehyde of formula (I) is prepared by acid hydrolysis of the sulfoxide of formula (II), the resulting reaction mixture can be directly used without isolating the compound of formula (II) therefrom.

The following Examples will illustrate the present invention in greater detail.

Example 1 2.65 g. of methyl 2-(p-methoxyphenyl)-l-methylthioethyl sulfoxide was dissolved in 50 ml. of methanol, and with the addition of 20 ml. of 1N sulfuric acid, the solution was heated for 6 hours at 50 C. The reaction mixture was concentrated at reduced pressure to 20 ml., and extracted with ether ml., two times). The extracted layer was washed with water and then with an aqueous solution of sodium hydrogencarbonate, and dried with anhydrous sodium sulfate. It was then concentrated at reduced pressure, and the residue was subjected to column NMR (in CCl.;):

6 3.50 doublet (2H, J=2.7 Hz.), 3.77 singlet (3H), 6.91A B quarter (4H, J=8.7 Hz.), 9.58 triplet (1H, J=2.7 Hz.).

Elemental analysis for C H O Calculated: C, 71.98; H, 6.71%. Found: C, 71.13; H, 6.61%.

Example 2 r 764 mg. of methyl 2-(p-methoxyphenyl)-l-methylthioethyl sulfoxide was dissolved in 6 ml. of ethanol, and with the addition of 1.03 ml. of ethyl orthoformate and, 5 drops of concentrated sulfuric acid, the solution was stirred for 27 hours at room temperature. 10 ml. of water 0 was added, and the reaction mixture was extracted with methylene chloride. The product was dried with anhydrous sodium sulfate, and concentrated at reduced pressure to give a diethyl acetal of p-methoxyphenylacetaldehyde. 5 ml. of ether was added to the acetal, and ml. of 0.25N dilute sulfuric acid was further added. The mixture was stirred for 12 hours at room temperature. The stirred mixture was then extracted with ether, and the ether layer was dried with anhydrous sodium sulfate, fol lowed by concentration at reduced pressure. The residue was subjected to column chromatography to give 386 mg. of p methoxyphenylacetaldehyde as a colorless liquid. Yield 82%.

Example 3 145 mg. of methyl Z-(p-methoxyphenyl)-1-methylthioethyl sulfoxide was dissolved in 5 ml. of ethanol, and with the addition of 2 ml. of 15N dilute sulfuric acid, the solution was allowed to stand for 11 hours at room temperature. The resulting p-methoxyphenylacetaldehyde was converted by a customary method to 2,4-dinitrophenylhydrazone, and analyzed quantitatively. Amount yielded 140 mg.; Yield 72%.

Example 4 v NMR (C01 6 1.13 triplet (6H, 1:135 Hz.), 2.77 doublet (2H, J =5 .7 Hz.), 3.42 quarter (2H, J=13.5 Hz.), 4.48 triplet (1H, 1:5.7 Hz.),

7.18 AB quartet (4H, 1:8.7 Hz.).

This acetal was subjected to the same procedure as described in Example 2 to give p-bromophenylacetaldehyde. This acetaldhyde was converted by a customary method to 2,4-dinitrophenylhydrazone having a melting point of 155l56 C. (recrystallized from ethanol).

Elemental analysis for C H BrO N Calculated: C, 44.15; H, 2.86; N, 14.77%. Found: C, 44.34; H, 2.92; N, 14.78%.

Example 5 123 mg. of methyl 2-(p-bromophenyl)-1-methylthioethyl sulfoxide was dissolved in 3.5 ml. of ethanol, and with the addition of 1.5 ml. of 15N dilute sulfuric acld,

6 the solution was allowed to stand overnight at room temperature. The resulting p-bromophenylacetaldehyde was converted by a customary method to 2,4-dinitrophenylhydrazone, and quantitatively analyzed. Amount yielded 126 mg. Yield 79.1%. The product was identified by infrared spectrography.

Example 6 270 mg. of methyl 1-methylthio-Z-phenylethyl sulfoxide was dissolved in 4 ml. of ethanol, and with the addition of 0.390 ml. of ethyl orthoformate and 3 drops of concentrated sulfuric acid, the solution was heated at 54 C. for 1.5 hours. 500 mg. of sodium hydrogen-carbonate was added, and the mixture was stirred for 30 minutes at room temperature, followed by concentration at reduced pressure. 10 ml. of methylene chloride was added to the residue, and the mixture was filtered. The filtrate was concentrated at reduced pressure to give 225 mg. of light yellow liquid. By simple distillation (oil bath temperature C./l4 mm. Hg), 198 mg. of a colorless liquid was obtained. This liquid was identified as a diethyl acetal of phenylacetaldehyde by the comparison of its infrared spectrum with that of the standard specimen. Yield 88.4%.

Example 7 72 mg. of methyl 1-methylthio-Z-phenylethyl sulfoxide was dissolved in 2.5 ml. of ethanol, and with the addition of 0.5 ml. of lSN dilute sulfuric acid, the solution was allowed to stand at room temperature for 12 hours. The resulting phenylacetaldehyde was converted in a customary manner to 2,4-dinitrophenylhydrazone, and quantitatively analyzed. Amount yielded 73 mg. Yield 68.9%. The identification of the product was performed using infrared spectroscopy.

Example 8 1.30 g. of methyl 2-(3,4-isopropylidenendioxyphenyl)- l-methylthioethyl sulfoxide was dissolved in 20 ml. of tetrahydrofuran, and with the addition of 5 drops of concentrated sulfuric acid, the solution was heated at 50 C. for 9 hours. Since the unreacted reactant remained in a small amount, 5 drops of concentrated sulfuric acid was further added, and the mixture was stirred for 12 hours at room temperature. 1 ml. of water and an excess of sodium bicarbonate were added, and the mixture was stirred for 30 minutes, followed by filtration, and concentrated at reduced pressure. The product was subjected to column chromatography (silica gel, benzene and methylene chloride) to give 297 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde in a yield of 34.0%.

The product was converted to an adduct of it with sodium hydrogensulfite, and the adduct was converted into the aldehyde, followed by purification by distillation under reduced pressure. This product was used for analysis.

C./3 mm. Hg colorless liquid, IR (neat):

172s cm.- NMR (CCl.,):

6 1.65 singlet (6H), 3.45 doublet (2H, J=3.7 Hz.), 6.55 m. (3H), 9.59 triplet (1H, J=3.7 Hz.). Elemental analysis for C H O Calculated: C, 68.73; H, 6.29%. Found: C, 69.01; H, 6.27%.

Example 9 1.014 g. of methyl 2-(3,4-isopropylidenedioxyphenyl)- l-methylthioethyl sulfoxide was dissolved in 20 ml. of methanol, and with the addition of 2 ml. of 4N dilute sulfuric acid, the solution was heated at 40 C. for 10.5 hours. The reaction mixture was neutralized with sodium bicarbonate, dried with anhydrous sodium sulfate, and

' 7 concentrated at reduced pressure. The product was subjected to column chromatography (silica gel, benzene) to give 213 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde and 153 mg. of a dimethyl acetal of (3,4-isopropylidenedioxyphenyl)acetaldehyde. The yield of the (3,4-isopropylidenedioxyphenyl)acetaldehyde was 31.3%, and the yield of the dimethyl acetal was 18.1%. The nuclear magnetic resonance of the dimethyl acetal was as follows:

NMR (CCI 6 1.61 singlet (6H), 2.67 doublet (2H,J=7.2 Hz.), 3.24 singlet (6H), 4.34 triplet (1H, J=7.2 Hz.), 6.49 singlet (3H).

Example 10 740 mg. of methyl 2-(3,4-isopropylidenedioxyphenyl)- l-methylthioethyl sulfoxide was dissolved in 10 ml. of methylene chloride, and with the addition of 10 drops of concentrated hydrochloric acid, the solution was stirred at room temperature for one hour and 40 minutes. The reaction mixture was neutralized with sodium bicarbonate, dried with anhydrous sodium sulfate, and concentrated at reduced pressure. The product was subjected to column chromatography (silica gel, benzene) to give 187 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde in a yield of 37.7%.

Example 11 868 mg. of methyl 2-(3,4-isopropylidenedioxyphenyl)- l-methylthioethyl sulfoxide was dissolved in 10 ml. of methanol, and with the addition of ml. of 1N aqueous solution of sulfuric acid, the solution was heated at 45- 50 C. for 4 hours. 20 ml. of Water was added, and the reaction mixture was neutralized with sodium bicarbonate and extracted three times with 150 ml. of ether. The ether layer was dried with anhydrous sodium sulfate, and concentrated at reduced pressure. The product was subjected to column chromatography (silica gel, benzene and methylene chloride) to give 180 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde in a yield of 49.0%.

:Example 12 1.166 g. of phenyl 2-(3,4-isopropylidenedioxyphenyl)- l-phenylthioethyl sulfoxide was dissolved in ml. of tetrahydrofuran, and with the addition of '5 drops of concentrated hydrochloric acid, the solution was allowed to stand for hours at room temperature. 50 ml. of ether was added for extraction purposes, and the extracted layer was washed with water, and then with an aqueous. solution of sodium bicarbonate. The extract was' dried with anhydrous sodium sulfate, concentrated at reduced pressure, and then subjected to column chromatography to give 240 mg. (yield 44.4%) of (3,4-isopropylidenedioxyphenyl acetaldehyde.

Example 13 234 mg. of methyl 2-(3,4-isopropylidenedioxyphenyl)- l-methylthioethyl sulfoxide was dissolved in 15 ml. of benzene, and the solution was heated under reflux for 3.5 hours. After concentrating the reaction mixture at reduced pressure, the product was subjected to column chromatography (silica gel, benzene) to give 39 mg. of (3,4-isopropylidenedioxyphenyl acetaldehyde.

Example 14 987 mg. of methyl 2-(3,4-isopropylidenedioxyphenyl)- l-methylthioethyl sulfoxide was dissolved in 8 ml. of ethanol, and with the addition of 1.3 ml. of ethyl orthoforrnate and 6 drops of concentrated sulfuric acid, the solution was stirred at room temperature for 40 hours. 10 ml. of water was added, and the reaction mixture was extracted with methylene chloride. The organic layer was dried with anhydrous sodium sulfate, and concentrated at reduced pressure. 5 ml. of tetrahydrofuran and ml.

of 0.25N dilute sulfuric acid were added to the residue, and the mixture was stirred for 19.5 hours at room temperature, followed by extraction with methylene chloride. The organic layer was dried with anhydrous sodium sulfate, concentrated at reduced pressure, and then subjected to column chromatography (silica gel, benzene) to give 432 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde in a yield of 65%.

Example 15 2.05 g. of phenyl 2-(3,4-isopropylidenedioxyphenyl)-lphenylthioethyl sulfoxide was dissolved in 20 ml. of ethanol, and with the addition of 10 drops of concentrated sulfuric acid and 1.8 ml. of ethyl orthoformate, the solution was stirred at room temperature for 50 hours. 15 ml. of water was added, and the reaction mixture was extracted with methylene chloride. The organic layer was dried with anhydrous sodium sulfate, and concentrated at reduced pressure. 10 m. of tetrahydrofuran and 30 m1. of 0.25N sulfuric acid were added to the residue, and the mixture was stirred for 24 hours at room temperature, followed by extraction with methylene chloride. The organic layer was dried with Glaubers salt, and concentrated at reduced pressure. The resulting residue was subjected to column chromatography (silica gel, benzene and n-hexane) to give 580 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde in a yield of 60% Example 16 2.08 g. of methyl 2-(3,4 methylenedioxyphenyl)-lmethylthioethyl sulfoxide was dissolved in 20 ml. of 1,2- dimethoxyethane, and with the addition of 1.71 g. of cupric chloride dihydrate, the solution was refluxed for 15 minutes. The solvent was removed by evaporation at reduced pressure, and 50 ml. of methylene chloride was added. The insoluble matter was removed by filtration. The filtrate was concentrated at reduced pressure, and subjected to column chromatography (silica gel, benzene) to give 722 mg. of (3,4-methylenedioxyphenyl) acetaldehyde in a yield of 45%.

The following Examples 17 to 26 illustrate the production of sulfoxides of formula (II) by reacting halocompounds of formula (III) with compounds of formula (IV). The sulfoxides of formula (II) obtained by these Examples can be converted to aldehyde of formula (I) by acid hydrolysis in the same way as described in Examples 1 to 16.

' Example 17 1.175 g. of methyl methylthiomethyl sulfoxide was dissolved in 5 ml. of tetrahydrofuran, and under cooling with ice, 0.965 g. (one equivalent) of sodium hydride Was added. The mixture was then stirred for one hour. 1.93 g. of p-methoxybenzyl bromide (1 equivalent) was added, and the mixture was stirred for 22 hours at room temperature, followed by addition of 40 ml. of methylene chloride and 2 ml. of water. The reaction mixture was dried with sodium sulfate anhydride, and concentrated at reduced pressure. The residue was subjected to column chromatography (silica gel, methylene chloride) to give 1.163 g. of methyl 2-(p-methoxyphenyl)-1-methylthioethyl sulfoxide in a conversion yield of 79.1%.

It was confirmed by IR and NMR that this product is a 1:1 mixture of two diastereomers.

IR (film):

11 SO 1037 cm.-

NMR (CDCl 6 7.05 A B quartet (4H),

. 3.81 singlet (3H),

3.8-2.2 m. (3H), 2.74 singlet (3/ 2H), 2.61 singlet (3/2H), 2.17 singlet (3/2H), 2.14 singlet (3/2H).

9 Example 18 590 mg. of methyl methylthiomethyl sulfoxide was dissolved in ml. of tetrahydrofuran, and under cooling with ice, 171 mg. (1.5 equivalents) of sodium hydride was added. The mixture was stirred for one hour. 813 mg. of benzyl chloride was added, and the mixture was stirred at room temperature for 15 hours. 50 ml. of methylene chloride and 1 ml. of water were added, and the reaction mixture was dried with anhydrous sodium sulfate, and the organic layer was concentrated at reduced pressure. The residue was subjected to column chromatography (silica gel, methylene chloride and ethyl acetate) to give 659 mg. of methyl 1-methylthio-2-phenylethyl sulfoxide in a conversion yield of 92.2%.

NMR (C01 6 7.22 singlet (5H), 3.8-2.2 m. (3H), 2.63 singlet (3/2H), 2.48 singlet (3/2I-I), 2.14 singlet (3/2H), 2.09 singlet (3/2H).

Example 19 1.182 g. of methyl methylthiomethyl sulfoxide was dissolved in 5 m1. of tetrahydrofuran, and under cooling with ice 229 mg. (1.0 equivalent) of sodium hydride was added. The mixture was stirred for one hour. 1.91 g. of p-bromobenzyl bromide (0.8 equivalent) was added, and the mixture was further stirred for 13 hours at room temperature. 50 ml. of methylene chloride was added, and the resulting precipitate was filtered. The filtrate was concentrated at reduced pressure, and subjected to column chromatography (silica gel, methylene chloride) to give 698 mg. of methyl 2-(p=bromophenyl)-1-methylthioethyl sulfoxide in a yield of 36.5%.

NMR (CDCl;,):

6 7.32 A B quartet (4H), 3.82.2 m. (3H), 2.77 singlet (3H), 2.13 singlet (3H).

Example 20 1.284 g. of methyl methylthiomethyl sulfoxide was dissolved in ml. of tetrahydrofuran, and under cooling with ice, 324 mg. of sodium hydride was added. The mixture was stirred for one hour. Then, 2.545 g. of 3,4- isopropylidenedioxybenzyl bromide was added, and the mixture was stirred for 19.5 hours at room temperature. 50 ml. of methylene chloride was added, and the resulting precipitate was separated by filtration. The filtrate was concentrated at reduced pressure, and subjected to column chromatography (silica gel, methylene chloride) to give 1.152 g. of methyl 2-(3,4-isopropylidenedioxyphenyl)-1- methylthioethyl sulfoxide.

Example 21 2.00 g. of methyl methylthiomethyl sulfoxide was dissolved in 10 ml. of tetrahydrofuran, and under cooling with ice, 388 mg. of sodium hydride was added, and the mixture was stirred for one hour, followed by heating at 50 C. for 20 minutes. The temperature was lowered to room temperature, and 3.17 g. of 3,4-isopropylidenedioxybenzyl bromide was added, and the mixture was stirred for 19 hours. 50 ml. of methylene chloride was added, and the resulting precipitate was filtered. The filtrate was concentrated at reduced pressure, and then subjected to column chromatography (silica gel, methylene chloride) to give 1.485 g. of methyl 2-(3,4-isopropylidene dioxyphenyl)-1-methylthioethyl sulfoxide.

Example 22 3.02 g. of methyl methylthiomethyl sulfoxide was dissolved in 10 ml. of tetrahydrofuran, and under cooling with ice, 760 mg. of sodium hydride was added. The mixture was stirred for minutes, followed by further 10 stirring for 15 minutes at room temperature. 7.30 g. of 3,4-isopropylidenedioxybenzyl bromide was added, and the mixture was stirred for 17.5 hours at 30 C. 50 ml. of methylene chloride was added, and the resulting precipitate was filtered. The filtrate was concentrated at reduced pressure, and subjected to column chromatography to give 4.41 g. of methyl 2-(3,4-isopropylidene dioxyphenyl)-l-methylthioethyl sulfoxide (conversion yield 73.5%). This sulfoxide is a mixture of two stereo isomers in a proportion of about 1:1 as determined by NMR. By crystallization from carbon tetrachloride, one of the stereoisomers could be isolated.

Colorless crystals m.p. l07.5108.5 C.

NMR (CDCl;,):

6 1.68 singlet (6H), 2.17 singlet (3H), 2.75 singlet (3H), 3.2-3.8 m. (3H), 6.69 singlet (3H), IR (KBr):

Elemental analysis for C H O S Calculated: C, 54.51; H, 6.34; S, 22.39. Found: C, 54.28; H, 6.20; S, 22.28.

Example 23 2.13 g. of methyl methylthiomethyl sulfoxide was dissolved in 7.5 ml. of tetrahydrofuran, and under cooling with ice, 413 mg. of sodium hydride was added. The mixture was stirred for 30 minutes under cooling with ice, and for another 30 minutes at room temperature, followed by addition of 3.23 g. of 3,4-isopropylidenedioxybenzyl bromide. The mixture was stirred for 14 hours at room temperature, and for 2 hours at 30 C. ml. of methylene chloride and 2 ml. of water were added, and the resulting mixture was dried with anhydrous sodium sulfate. After filtration, the filtrate was concen trated at reduced pressure, and the residue was subjected to column chromatography (silica gel, methylene chloride) to give 2.42 g. of methyl 2-(3,4-isopropylidenedioxyphenyl) -1-methylthioethyl sulfoxide.

Example 24 1.30 g. of methyl methylthiomethyl sulfoxide was dissolved in 5 ml. of tetrahydrofuran, and a tetrahydrofuran solution containing 1.057 g. of phenyl lithium was added. The mixture was stirred for 30 minutes under cooling with ice, and for 30 minutes at room temperature, followed by adding 1.92 g. of 3,4-isopropylidenedioxyphenyl chloride. The mixture was stirred for one hour at room temperature, 13 hours at 35 C., and for additional 8.5 hours at 48 C. 50 ml. of methylene chloride was added, and the resulting precipitate was filtered. The filtrate was concentrated at reduced pressure, and then subjected to column chromatography (silica gel, methylene chloride) to give 619 mg. of methyl 2-(3,4-isopropylidenedioxyphenyl)-1-methylthioethyl sulfoxide.

Example 25 Example 25 was repeated except that butyl lithium was used instead of the phenyl lithium as a 20% n-hexane solution in an amount of 5.8 ml. There was obtained 575 mg. of methyl 2-(3,4-isopropylidenedioxyphenyl)-l-methylthioethyl sulfoxide.

Example 26 2.48 g. of phenyl phenylthiomethyl sulfoxide was dissolved in 10 ml. of tetrahydrofuran, and under cooling with ice 240 mg. of sodium hydride was added. The mixture was stirred for one hour. 2.43 g. of 3,4-isopropylidenedioxybenzylbromide was added, and the mixture was stirred for 18 hours at room temperature. 50 ml. of methylene chloride was added, and the resulting precipitate was filtered. The filtrate was concentrated at reduced pressure, and subjected to column chromatography (silica gel, methylene chloride) to give 3.44 g. of phenyl 2-(3,4- isopropylidenedioxyphenyl)-1-phenylthioethyl sulfoxide.

The following Example illustrates the production of the aldehyde of formula (I) by reacting the halocompound of formula (III) with the compound of formula (IV) to form the sulfoxide of formula (II), and subjecting the resulting reaction mixture to acid hydrolysis without isolating the sulfoxide therefrom.

Example 27 1.80 g. of isopropyl isopropylthiomethyl sulfoxide was dissolved in 15 ml. of tetrahydrofuran, and under cooling with ice, 240 mg. of sodium hydride was added, and the solution was stirred for one hour. 2.31 g. of 3,4-dimethoxybenzyl bromide was added, and the mixture was stirred for 20 hours at room temperature, and for 3 hours at 35 C. 100 ml. of methylene chloride was added. After separating the insoluble matter by filtration, the filtrate was concentrated at reduced pressure. The residue was dissolved in 20 ml. of tetrahydrofuran, and with the addition of 10 drops of concentrated sulfuric acid, the solution was stirred for 10 hours at 50 C. 500 mg. of sodium bicarbonate was added, and the mixture was stirred for 30 minutes at room temperature. Then, the insoluble matter was separated by filtration. The filtrate was concentrated at reduced pressure, and the residue was subjected to column chromatography to give 631 mg. of (3,4-dimethoxyphenyl)acetaldehyde in a yield of 35%.

The following example shows the preparation of Dopa by the Strecker reaction of (3,4-isopropylidenedioxyphenyl)acetaldehyde, which is one of the aldehyde products in accordance with the present invention.

8 ml. of methanol and 4 ml. of water were added to 477 mg. of (3,4-isopropylidenedioxyphenyl)acetaldehyde, and 240 mg. of sodium cyanide was further added. The mixture was acidified with 1N dilute sulfuric acid, and then rendered weakly alkaline with 4N-sodiumhydroxide aqueous solution. The mixture was then stirred for one hour at C., and then for 10 hours at room temperature. The reaction mixture was extracted with methylene chloride. The organic layer was dried with anhydrous sodium sulfate, and concentrated at reduced pressure to give 538 mg. of a light yellow oily matter. It was confirmed from IR and NMR that this product is 2-hydroxy-3-(3',4'-isopropylidenedioxyphenyl propionitrile.

535 mg. of the 2-hydroxy-3-(3,4'-isopropylidenedioxyphenyl)propionitrile was dissolved in 3 ml. of methanol, and the solution was saturated with ammonia gas. The solution was allowed to stand for 4 hours at room temperature. 5 ml. of water was added, and the resulting mixture was extracted with ether. The ether layer was washed with water, dried with anhydrous sodium sulfate, and concentrated at reduced pressure to give 487 mg. of a light yellow oily matter. For analytical purposes, a part of the oily matter was purified. It was confirmed from IR and NMR that this product is 2-amino-3-(3,4'-isopropylidenedioxyphenyl propionitrile.

IR (film):

3370, 3300, 1607, 1500, 1449, 1380, 1258, 1238, 1220, 1160, 982, 838 cm.- NMR (CDCl 6 1.67 singlet (6H), 1.5-2.0 broad peak (2H), 2.92 doublet (2H, J :67 Hz.), 3.89 triplet (1H, J=6.7 Hz.), 6.67 singlet (3H).

225 mg. of the above 2-amino-3-(3',4'-isopropylidene dioxyphenyl)propionitrile was dissolved in 5 ml. of 6N- hydrochloric acid, and the solution was refluxed for 2 hours. The reaction mixture was concentrated at reduced pressure to about one milliliter. It was saturated with ammonia gas, concentrated at reduced pressure, dried, and washed with hot alcohol to give 178 mg. of 3-(3',4'- dioxyphenyD-DL-alanine having a melting point of 233- 245 C. (decomp.). The yield was 88%. By recrystallizing the product from water, a pure product having a melting point of 265-268 C. (decomp.) was obtained. The identification was performed using the standard specimen, IR, mixture melting point, and paper chromatography.

What is claimed is:

1. A method of preparing an aldehyde of the formula wherein R is a member selected from the group consisting of hydrogen and alkoxy having 1 to 4 carbons, R is a member selected from the group consisting of hydrogen, halogen and alkoxy having 1 to 4 carbons, and R and R together represent alkylidenedioxy having 1 to 4 carbons; which comprises the steps of subjecting to an acidic hydrolysis a sulfoxide of the formula wherein R and R have the above meanings, and the two R groups are the same and each selected from the group consisting of alkyl having 1 to 4 carbons and phenyl, said acidic hydrolysis being carried out in the presence of mineral or organic protic acids having a pK smaller than about 1 or Lewis acids.

2. The method of claim 1, wherein said acidic hydrolysis is carried out at 9 to C. in an organic medium which is chemically inert to the compounds of formula (I) and (II).

References Cited Schultz, et al., Chemical Abstracts, Vol. 73 (1970), col. 98748e.

Ogura, et al., Chemical Abstracts, Vol. 75 (1971), col. 118070z.

DONAL-D G. DAUS, Primary Examiner I. H. TURNIPSEED, Assistant Examiner US. Cl. X.R. 

1. A METHOD OF PREPARING AN ALDEHYDE OF THE FORMULA 